There are many types of electrical systems that benefit from electrical isolation. Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow, meaning that no direct electrical conduction path is permitted between different functional sections. As one example, certain types of electronic equipment require that high-voltage components (e.g., 1 kV or greater) interface with low-voltage components (e.g., 10V or lower). Examples of such equipment include medical devices and industrial machines that utilize high-voltage in some parts of the system, but have low-voltage control electronics elsewhere within the system. The interface of the high-voltage and low-voltage sides of the system relies upon the transfer of data via some mechanism other than electrical current.
Other types of electrical systems such as signal and power transmission lines can be subjected to voltage surges by lightning, electrostatic discharge, radio frequency transmissions, switching pulses (spikes), and perturbations in power supply. These types of systems can also benefit from electrical isolation.
Electrical isolation can be achieved with a number of different types of devices. Some examples of isolation products include galvanic isolators, opto-couplers, inductive, and capacitive isolators. Previous generations of electronic isolators used two chips in a horizontal configuration with wire bonds between the chips. These wire bonds provide a coupling point for large excursions in the difference between the grounds of the systems being isolated. These excursions can be on the order of 25,000 V/usec.
As mentioned above, electrical isolation can be achieved with capacitive, inductive isolators, and/or RF isolators to transmit data across an isolation boundary. The capacitive approach may employ a small capacitor, say 100 fF across the isolation boundary. For the receiver to discern logic level swings differentiated across the isolation boundary, the receiver needs to detect the transmitted signal in the presence of large excursions that have roughly the same bandwidth of interest.
Prior capacitive isolators use a planar package design in which two chips are separated in the horizontal direction and the coupling device is connected via chip-to-chip wire bond(s). The prior solutions may have the coupling device integrated into the receiver or they may employ a third chip that has the coupling device. In either scenario, the wire bond acts like an antenna with about 1-2 nH of inductance. This inductor is suspended over the isolation boundary and has a certain coupling to the ground planes of both chips. Since most couplers are differential, there are at least two of these wire bonds. If the coupling to these wire bonds is not balanced, then the large common mode rejection excursions (e.g., 1000V at rate of 25,000V/usec) will turn into differential voltages via this unbalanced coupling.
It would be desirable to employ a capacitive isolator that minimizes the coupling to this node by removing the wire bonds and making this node as short as possible. It would also be desirable to achieve these goals without increasing production costs to the point where high-volume production is not feasible.